The invention relates generally to a system and process for sulfur recovery and particularly to a system and process for sulfur recovery from a sulfur-laden gaseous stream.
Coal derived synthesis gas (“syngas”) or other feedstocks such as biogas, waste gas, and blast furnace gas can be used effectively for the applications such as power generation and chemicals production. In an integrated gasification/combined cycle (IGCC) process, coal is gasified with air (or oxygen) and steam to produce a combustible gas (coal gas) comprising principally carbon monoxide, carbon dioxide, hydrogen, methane, water vapor and nitrogen (when air is used as the oxidant). The gases serve as fuel to a gas turbine or a gas turbine-steam turbine combined cycle to generate electrical power. The product of the IGCC process can also contain minor amounts of other gaseous species. Other feedstock such as biogas, waste gas, and blast furnace gas can produce different gaseous compositions than the coal gases. However, the coal gas or other feedstocks as described above are generally purified to remove species such as particulate matter, alkali metals, and sulfur compounds before being considered for the intended end use. The sulfur compounds in such gases include hydrogen sulfide (H2S) and, in lesser amounts, carbonyl sulfide (COS), carbonyl disulfide (CS2) and the like, depending on the sulfur content of the feedstock from which the gas is derived and derivation process used. In order to meet environmental standards and to prevent damage to equipment further using the combustible gas or other feedstocks, it may be necessary to remove some or all of the sulfur compounds and other contaminants from the gases.
One process of removing sulfur compounds from a sulfur-laden gas stream includes desulfurization through the contact of sulfur compounds with a sorbent, such as a metal oxide for example, to form metal sulfides, also referred to herein as sulfurized mass. The net sulfur sorption reaction is given by an example as in the equation (1) below:H2S+MO→MS+H2O  (1)wherein M is the metal present in the sorbent; MO represents the metal oxide; and MS represents the metal sulfide. For the sake of simplicity, M is represented as divalent, but it will be apparent that metals in other valence states may also be employed. Also, since the actual proportion of sulfur in the metal sulfide usually varies from theory, these equations may not accurately represent the stoichiometry of the reactions.
Following the desulfurization, the sorbent is regenerated in a regenerator to recover metal oxide. The standard approach to the regeneration of this sorbent is by the desorption of absorbed, adsorbed, or reacted sulfur or sulfur compounds by oxidation or roasting, to yield the metal oxide and sulfur containing gas. Oxidation can be facilitated by supplying regeneration gas to the sulfurized mass to regenerate the metal oxide. The regeneration reaction may be represented by the following equation (2):2MS+3O2→2MO+2SO2  (2)wherein M, MS and MO are as defined above. It is apparent that during this regeneration, gaseous forms of sulfur or sulfur-containing species will be evolved along with other gases, and must be controlled to avoid additional pollution problems.
Depending on the regeneration method employed, gaseous sulfur species can be in the form of oxides of sulfur, carbonyl sulfide and carbonyl disulfide among others. Furthermore, some sulfurized mass can be regenerated to produce gaseous sulfur species in the reduced form such as hydrogen sulfide, when contacted with regenerator gases other than oxygen or air. For instance, tin sulfide (SnS), when contacted with steam, is regenerated to stannic oxide with the evolution of hydrogen sulfide and hydrogen gases.
The concentration of gaseous sulfur species in the sulfur-containing gas stream of the regenerator is ordinarily low, typically less than about 10%. It is advantageous to have the gaseous sulfur contents in the sulfur-containing gas stream as high as possible for effective production or recovery of saleable forms of sulfur from the sulfur containing gas stream before releasing it as the tail gas to the atmosphere. The present invention provides a system and method for efficiently recovering sulfur from the sulfur stream of the regenerator.